Examples of orthoalkylated phenols used in industrial fields include 2, 6-xylenol as a raw material for producing polyphenylene oxide resins, 2,3,6-trimethylphenol as a starting material for synthesizing vitamin E,.and o-cresol, 2,5-xylenol, 2,3-xylenol, 2,4-xylenol, 2,4,6-trimethylphenol, methylhydroquinone or the like as a starting material or an intermediate of medicine, agricultural chemicals, resins, various additives, industrial chemicals, etc.
Methods of orthoalkylating a phenol having a hydrogen atom of at least one ortho position thereof with an alkyl alcohol in the presence of an alkylation catalyst are known in the art. In these methods, a phenol is reacted with an alkyl alcohol in a vapor phase in the presence of a catalyst composed only of magnesium oxide, a catalyst composed of magnesium oxide coated with copper, or a catalyst composed of magnesium oxide and a co-catalyst of manganese salt as bases.
The catalyst composed only of magnesium oxide is, for example, the magnesium oxide catalyst described in Japanese Patent Publication No. 42(1967)-6894, which is prepared by compression molding powder of basic magnesium carbonate and calcining the molding.
The catalyst composed of magnesium oxide coated with copper is, for example, the catalyst composition described in Japanese Patent Laid-open Publication No. 59(1984)-228940, which comprises magnesium oxide containing copper about 0.1% by weight based on magnesium oxide, wherein this copper is adhered on magnesium oxide either, the copper being either in elemental form being a shape of a layer of submicroscopic thickness or in chemically bonded form. This catalyst composition is prepared by first preparing at about 50 to 100° C. a slurry, in an aqueous solution, of at least one copper salt of a substantially water insoluble magnesium reagent capable of forming magnesium oxide upon calcination (at least one member of magnesium oxide, magnesium hydroxide and magnesium carbonate), subsequently controlling the copper content of the slurry to thereby obtain a magnesium-containing solid layer having a copper coating of submicroscopic thickness, and thereafter drying the solid layer and effecting calcination thereof.
The catalyst composed of magnesium oxide and a co-catalyst of manganese salt as bases is, for example, the catalyst composed of magnesium oxide and manganese sulfate described in Japanese Patent Publication No. 46(1971)-21371. This catalyst is prepared either by pulverizing magnesium oxide and mixing the resultant powder with manganese sulfate or by impregnating magnesium oxide with manganese sulfate and subjecting the impregnated magnesium oxide to drying, molding and calcining.
These conventional orthoalkylation catalysts for phenols containing magnesium oxide are industrially employed, for example, in the production of 2,6-xylenol from phenol as a starting material. They, although thus meeting the objective to a certain extent, suffer from the degradation as-inherently exhibited by magnesium oxide containing catalysts. Therefore, further enhancement of the catalytic performance thereof is demanded from the industrial point of view.
In Japanese Patent Laid-open Publication No. 7(1995)-265710, the same applicant disclosed, as a catalyst of high selectivity that exhibits catalytic performance improved over the conventional magnesium oxide containing catalysts, an orthoalkylation catalyst for phenols produced by calcining a catalyst precursor composed of a dry mixture of manganese oxalate (a), fine particles of a phenol resin (b) and at least one magnesium compound selected from among basic magnesium carbonate and magnesium oxide.
However, there is a demand for the development of an orthoalkylation catalyst for phenols which is superior to this catalyst in respect of activity, selectivity, catalytic life and stability, and further the development of a process for producing an orthoalkylated phenol with the use of the above orthoalkylation catalyst.
Therefore, the objective of the present invention is to provide an orthoalkylation catalyst for phenols which exhibits high activity and high selectivity, has prolonged catalytic life and is stable, and to provide a process for producing an orthoalkylated phenol with the use of the orthoalkylation catalyst.